Sorption Kinetics and Intraparticle Diffusivities of Cd (II) and Fe (III) Ions on Unmodified Snail Shell Powder

Sorption kinetics of Cd (II) and Fe (III) ions in aqueous solution by unmodified snail shell powder was carried out through time dependent studies. Maximum percent adsorption capacity of the metal ions based on contact time was found to be 62.3% and 58.74% for Cd and Fe respectively at 60 minutes. The kinetic behaviour of the metal ions towards the adsorbent was studied with seven kinetic and diffusion models: pseudo-first order and pseudo-second order, mass transfer kinetics, intraparticle diffusion (external film, particle diffusion and penetrant transport). The pseudo first order rate constants k1 (g/mg min) were determined to be 2.203 x 10-3, for both Cd (II) and Fe (III). The pseudo-second order rate constant, k2 for Cd and Fe (III) were found to be 2.256 x 10-2 and 2.792 x 10-1 g/mg min respectively. Sorption capacities based on the pseudo-first order model were found to be 4.7315mg/g and 6.4565mg/g for Cd (II) and Fe (III) respectively. Pseudo-second order sorption capacities for Cd (II) and Fe (III) were 5.3763 and 4.9261 respectively. Correlation coefficient R2, for Cd (II) and Fe (III) were greater than 0.99 for pseudo-second and greater than 0.95 for the pseudo-first order. All diffusion models used correlated well over 0.94 with a maximum of 0.9917 for the penetrant transport model for Cd (II) ion.